The sky scrapers here aren’t the problem. I’m pretty confident most if not all can withstand a big earthquake. It’s the few hundred thousand 4 to 8 floor buildings… quite often having been built before the latest Earthquake standards (which I believe was the late 80s).
Uggh… this is worse than I thought. Here’s some lovely excerpts from here which is a reflection of what would happen in current day Tokyo if another 1923-sized Earthquake hit. Note that more peopled died in the ensuing fires after the quake (including 14,000 people in one single location) than the quake itself.
There’s a Wikipedia entry somewhere that tries to calculate implications on the world economy if an Earth-shattering quake hit Tokyo. The truth of the matter is, not only does the majority of the population aggregate to this one spot on weekdays (w/ commuters included, you’ve got some 30-40 million people in Tokyo on any given day, which is 20-25% of the population), but the entire government body resides here. Most companies have their HQ in or near the area. It is redefinition of all eggs in one basket.